More than 900 of those flights had been preemptively canceled by late Tuesday and nearly all big U.S. carriers were waiving change fees for airports in the storm's path.

The hardest-hit airports on Wednesday were the three major airports serving Washington and Baltimore, where several inches of snow were expected before a switchover to ice and – eventually – rain.

At Washington Reagan National, nearly 370 combined arrivals and departures were canceled as of 7:35 p.m. ET, accounting for more than a third of the day’s entire schedule there. A similar percentage of the day’s flights also had been canceled at both Baltimore/Washington (BWI) and Washington Dulles airports.

Wednesday’s delays spread beyond the Washington and Baltimore area as wintry weather fell at airports from the Dakotas to the Ohio Valley and the Mid-Atlantic.

At the Minneapolis/St. Paul airport, a hub for Delta, flights were briefly halted as snow fell faster than crews could clear from runways. More than 130 flights had been canceled, affecting about 1 out of every 10 scheduled to fly there today. Of those not canceled, nearly half were delayed. Some arrivals were diverted to nearby airports such as Duluth, Minnesota, according to local media reports.

"The rate of snowfall is the challenge," airport spokesman John Welbes told The Associated Press.

At Philadelphia, more than 15 percent of the day’s flights had been canceled.

The New York City-area's delay-prone airport also saw problems, with about 20 percent of LaGuardia's flights canceled and about 15 percent at Newark, New Jersey. At JFK, close to 10 percent of the day's flights had been scrubbed.

Chicago also was another trouble spot, with about 16 percent of Wednesday's flights canceled at Midway Airport and about 12 percent at O'Hare.

Other airports seeing a spike in cancellations included St. Louis; Cleveland; Columbus, Ohio; Rochester, New York; Richmond, Virginia; Greensboro, North Carolina; and Madison, Wisconsin.

Another problem facing travelers on Wednesday was a spike in cancellations at Southwest that the carrier blamed on the mechanics’ union. Southwest and the union have been in prolonged and occasionally contentious contract talks since 2012.

"We apologize to our customers who have been inconvenienced by this disruption,'' Southwest Chief Operating Officer Mike Van de Ven said late Tuesday.

Southwest had more than 440 cancellations on Wednesday, according to FlightAware. While many of those could be traced to airports experiencing poor weather, they remained unusually high at some airports.

A ramp worker opens up the front cargo door on an All Nippon Airways Boeing 777-300 after it arrived from Tokyo to Washington Dulles International Airport on June 29, 2018. Jeremy Dwyer-Lindgren, special to USA TODAY

A business jet taxies out for departure as a United Airlines Boeing 777 heads off into the evening from Washington Dulles International Airport on June 29, 2018. Jeremy Dwyer-Lindgren, special to USA TODAY

A mobile lounge controller directs the unique busses around Washington Dulles International Airport on June 29, 2018. The position is likely the only such in the U.S. Jeremy Dwyer-Lindgren, special to USA TODAY

Slips of paper note details on incoming international flights at Washington Dulles International Airport on June 29, 2018. Each will need mobile lounges to take the passengers to immigration control. Jeremy Dwyer-Lindgren, special to USA TODAY

Airport operations escorts the massive Airbus A380 as it taxies out for departure at Washington Dulles International Airport on June 29, 2018. The jet's wingspan is so large it can reach past the taxiway, presenting a risk of damaging equipment. Jeremy Dwyer-Lindgren, special to USA TODAY

Wheels still spinning, the undercarriage of a United Airlines Boeing 767-300 is sucked up into the belly after taking off from George Bush Intercontinental Airport in Houston on Jan. 27, 2019. Jeremy Dwyer-Lindgren for USA TODAY